Andrew Niccol has made it. Not because he’s written and directed “The Host,” based on the bestselling book by “Twilight” mastermind Stephenie Meyer. Not because he earned an Oscar nomination for scripting “The Truman Show,” which featured Jim Carrey in one of his first dramatic roles as a man whose entire life is a reality show. Not because he wrote and directed acclaimed sci-fi films like “Gattaca” and “S1m0ne,” movies whose premises about perfecting humans were way prescient for their time. No, Niccol is pleased to learn he has been immortalized on an episode of “The Simpsons.” The scene in question involves Homer cutting off his thumb and Marge telling him they can take it to the hospital to sew it back on. Homer’s response: “Re-attach a thumb? This isn’t ‘Gattaca,’ Marge!”

Hearing this, the New Zealand native lets out a warm chuckle. “I guess that’s some sort of accolade, when you’ve made it on ‘The Simpsons.’” But he can even top that. “Did you know there’s now a psychological condition named for ‘The Truman Show?’ It’s called ‘Truman Show Syndrome’ or ‘Truman Show’ delusion. It’s where people actually think that they’re in a reality show. It’s a literal condition. So I’m very proud, I have a mental disorder named after me.”

Niccol’s star is likely to rise even more when “The Host” hits theaters this Friday, Mar. 29. Set after a peaceful alien race takes over Earth, Saorise Ronan plays Melanie, a young woman whose body is taken over by an alien soul. Melanie is still in love with her boyfriend (Max Irons) while the soul sharing her body begins to fall for a fellow freedom fighter (Jake Abel). This love quadrangle plays out against the backdrop of some intense action as Melanie is hunted down after escaping.

How did you end up landing this coveted job?Andrew Niccol: It was kind of flattering. The producer asked Stephenie, “What sci-fi movies do you like?” And I had two of the five she mentioned—“Gattaca” and “The Truman Show.” I hadn’t read the book but as soon as I read it, it really grabbed me. I just loved the idea. And I can say that because it’s not my idea. This inner conflict with two spirits in one body at war with each other and they form an understanding and learn to co-exist and even love each other.

How involved was Stephenie as you wrote the script? Niccol: I wrote the first draft and sent it to her and she would make comments and send it back. There was some back and forth like that. I’d never adapted a book before and had no idea what to expect, but it was so wonderful. She’s almost like the alien souls in that she’s very calm and agreeable. Even if she disagrees with you, it’s done in such a polite way. She’s so normal—and for someone with so much success, she could easily not be normal!

Did you feel the pressure of pleasing this enormous fan base?Niccol: I was a little conscious of the fact it was such a loved book and I wanted to honor it and be faithful to it. But at a certain point I thought, “Ah just tell a great story, forget about the expectations.” But I’m very pleased with the screenings that they’ve had that people are happy that it is faithful to the book. But it has to work for all groups, even for people who have never heard of the book.

I have to imagine that from the start, Saorise Ronan was at the top of your list?Niccol: The thing about Saorise is there was almost no plan B. We throw around this phrase “The Real Deal” a lot but this girl is The Real Deal. She speaks with a thick Irish brogue and can turn it off like a switch. She has two different American accents in the movie, one for her human character, one for her alien character. The other thing is, she is so likeable onscreen—what you see is what you get with that girl. She didn’t have to audition. You watch “Atonement,” you watch “Hanna,” it’s like, “Where do you sign?”

What about rounding out the rest of this love triangle?Niccol: As soon as we had Saorise, it became quite an extensive auditioning process to find that chemistry. I always think you can fix the anatomy of a movie, but you cannot fix the chemistry. It’s either there or it’s not. And as soon as she was in a room with Max and Jake, it was obvious. Saorise’s dad Paul was in the room and we looked at each other and went, “Yep.”

Did you watch the “Twilight” films to see how other filmmakers handled adapting Stephenie’s work?Niccol: I actually got to go to the premiere of “Breaking Dawn: Part 1.” It was shocking to me. There was screaming and shrieking. It was actually really good because what I realized—and this happened in previews for “The Host” as well—is if you have a packed house with this audible reaction, you wouldn’t be able to hear the next line! So I added frames to the movie so you could hear the next line of dialogue. I actually lengthened a shot when I realized things would get a really big laugh or reaction.

How do you feel about the audition process?Niccol: It’s like dating for me. I kind of know in five seconds if there’s a chance. It’s a very strange thing. I once met with an actor and he was about to do a scene and he said, “Shall I do it?” And I said, “Actually, the audition’s over. You’ve got the role.” I just knew. I go with my instinct.

Can you say what movie it was for?Niccol: That was for “Gattaca.” An actor named Jude Law.